1. Field of the Invention
The present invention relates to a process for producing a multilayer molded article which comprises a core layer of a thermoplastic resin and a skin material which is laminated on the core layer.
2. Description of the Related Art
A large number of plastic molded articles are used in many fields including the automobile and domestic electric appliance fields because of their low costs, free moldability and light weight. However, they have some drawbacks that they have poor appearance and cool feeling and they tend to be easily flawed. Then, it is highly desired to impart decoration and soft feeling to the plastic molded articles. Hitherto, many attempts have been made to provide a compound which satisfies such desires. But, it is difficult to produce a resin molded article having improved surface properties while maintaining the free moldability and strength from a single material, and at present, a multilayer molded article comprising a combination of plural materials which have different functions is generally used.
Many proceses are known for the production of a multilayer molded article. For example, Japanese Patent Kokai Publication No. 13859/1976 discloses a process comprising preforming a skin material by, for example, thermoforming, placing the preformed skin material in a mold, supplying a core resin melt and then integrating the two together. This process requires many molding steps and much apparatus. In addition, since each apparatus and each molding method has its own technical problems, much work and expense are necessary to produce a final product.
As disclosed in Japanese Patent Publication No. 19132/1975, another process molds a multilayer molded article using a single mold having a vacuum molding function and core resin supplying means. But, this process is no better than the above process.
To overcome the drawbacks of the above two processes, Japanese Patent Kokai Publication No. 63461/1978 discloses a process comprising placing an unpreformed skin material in a mold and then integrating the skin material and the core resin. Though this process is economical, tension of the skin material is controlled only in one direction and not in other directions, the skin material tends to be wrinkled, so that this process can produce only a simple shape article but not a deep draw molded article.
As proposed in Japanese Patent Publication No. 24807/1988, a multilayer molded article can be produced by clamping edges of a skin material between a female mold and a skin material-fixing frame, preforming the skin material, supplying a melt of a thermoplastic resin as a core material and then molding the resin. However, this process is not necessarily satisfactory for molding a large size article, in particular, having a complicated shape.